The present invention relates to a tone source of rhythm which is designed to permit an arbitrary selection of a noise component and a pitch determining component as a tone source of cymbals or the like.
Heretofore, there have been proposed, for obtaining a tone source of cymbals or the like, a method of mixing pluralities of transistor noises and notes, a method using digital noises and so forth, but many of them are of the type employing either noise or pitch determining components only.
It has also been proposed to employ a noise generator composed of an N-stage shift register such as set forth in Japanese Pat. Appln. No. 115,393/78 "Noise Generator" now Laid-Open Publication 55-41464. As depicted in FIG. 1, outputs from first and Nth stages of an N-stage shift register 1, which is driven by clock pulses, are provided to an exclusive OR circuit 2, which yields an output "1" or "0" depending on whether the inputs are of the same or different levels. The output from the exclusive OR circuit 2 is fed back to the first stage of the shift register 1 via an OR circuit 3, thus obtaining 2.sup.N -1 pseudo-random pulses from the Nth stage output in one period. If N=8, then 2.sup.8 -1=255. If the clock pulses have a frequency of 100 KHz, then the repetitive frequency f of noise is as follows: ##EQU1## producing a noise having a frequency of 392.16 Hz.
FIG. 2 shows the noise thus obtained. The pulse train is a noise when it is produced for only one period, but it includes pitch determining components when repeated at a frequency of 392.16 Hz. These components vary with the number of stages of the shift register and the clock frequency. A decrease in the number of stages of the shift register decreases the noise component but increases the pitch determining component, whereas an increase in the number of stages of the shift register increases the former and decreases the latter.
Natural sounds of musical instruments such as cymbals and the like are more complex in the contents of the noise component and the pitch determining component, their mixing ratio and their repetitive frequencies. To obtain wide varieties of the contents and repetitive frequencies of these components, there has been proposed that outputs from a pluraity of noise generators which respectively yields random pulses in synchronism with different clock pulses and have different repetitive frequencies are provided via a nonlinear gate, for example, an AND gate, as set forth in Japanese Pat. Appln. No. 21380/80 "Rhythm Tone Source" now Laid-Open Publication 56-117289. This permits arbitrary and various selections of the noise and pitch determining components but the arrangement is fixed, and hence it has the problem that long-time playing may become monotonous.